Glare is the biggest impairment experienced by cataract patients. In nighttime driving, headlight glare may severely affect the safety of the driver and pedestrians. Overall reduction of conspicuity of the pedestrians and other driving related features (e.g. lane markers, traffic signs) affects cataract patients due to their reduced visual acuity (VA) and contrast sensitivity (CS). Although it is widely accepted that headlight glare caused by oncoming cars is a primary nighttime driving hazard, much less is known about how drivers are able to interact with glare from an oncoming car's headlights, and how this glare affects the driver's performance. Cataract is one of the few eye conditions where a patient's VA and CS can be restored to normal levels by surgical procedures. Therefore, the impact of glare from the oncoming headlight caused by cataract can be effectively studied, while factoring out other individual variability that affect nighttime driving, by measuring their nighttime driving behaviors and performances in progressive way along their corrective surgeries in a physically validated, novel, real-time headlight glare simulator that runs concurrently with a driving simulator. We plan to quantitatively measure the impacts of headlight glare on early-to-mid bilateral cataract patients in the following ways: 1) detection performance (hazard detection rates and reaction times), 2) vehicle control (speed, lane position, steering stability), and 3) ey and head movements (gaze movements toward and away from the glare), and their interactions with the other measures. We will measure driving performance and gaze movements of normally sighted subjects with or without simulated cataracts (Study 1); {a pilot group of patients with bilateral cataract (Study 2)}; bilateral cataract patients before (Study 3) and after cataract extraction surgery for the first eye (Study 4); and after their second surgery (Study 5). The data will be compared between with and without headlight glare conditions. In addition to the direct performance and behavioral comparisons, the power of the clinical vision function measures (e.g. VA, CS, photostress test, intraocular straylight measure) to predict actual driving performance, and the coherence between self-ratings of glare difficulties in real-world and in simulated conditions will be evaluated. The results will provide the first set of comprehensive data on the functional impact of oncoming headlight glare in cataract patients during nighttime driving, and will have widespread benefits, providing valuable guidance for cataract surgery, driver training, design of glare control devices, driver testing and driving regulations. Once the effects are successfully measured, the testing platform developed for the proposed studies can easily converted to a reliable evolutional tool for other vision conditions such as age-related macular degeneration (AMD), which is known to have glare complications including prolonged photo stress recovery. Also it can be used for measuring the safety of vision-aid devices and multifocal intraocular lenses during nighttime driving.